Some geological formations enable rotary drill rigs to form a relatively straight hole as a wellbore is drilled from the surface of the earth down to the payzone. Other formations, often referred to as crooked hole type formations, cause the drill bit and string to meander or deviate away from vertical as the borehole is drilled by the bit. Deviation from vertical sometimes become substantial, and in aggravated cases, the hole can match the inclined angle of the formation.
A crooked borehole is undesirable because it is difficult to case, and undue localized stresses and strains are placed here and there on the casing. Furthermore, should a pumpjack be used to produce the well, the sucker rod invariably will contact and scrape against the production tubing because of the crooked hole causing excessive wear and premature failure of the rod or tubing string.
In some instances, it is possible to minimize the deviation of the hole by closely controlling the bit weight and rotary table speed. Others skilled in the art have proposed to circumferentially space grooves about a drill collar as taught in Fox U.S. Pat. No. 3,146,611; Toelke U.S. Pat. No. 3,267,695; Arnold U.S. Pat. Nos. 3,391,749 and 4,068,730 which disclose an apertured drill collar which proportedly reduces the borehole deviation.
Fox U.S. Pat. No. 3,146,611 discloses grooves 23 radially and circumferentially spaced from one another. Toelke U.S. Pat. No. 3,267,695 and Arnold U.S. Pat. Nos. 3,391,749 and 4,068,730 show an apertured drill collar. Lari U.S. Pat. No. 3,525,237; Herring U.S. Pat. No. 3,519,090; Bobo U.S. Pat. No. 3,419,094; Schurman U.S. Pat. No. 3,411,321; Scarborough U.S. Pat. No. 3,237,427; Dunn U.S. Pat. No. 2,841,366; Thurston U.S. Pat. Re. No. 16,061; and Ortloff U.S. Pat. No. 3,338,069 are other examples which show the status of the art in this respect, and reference is made to these references for further background of the invention.
The present Hydraulic Straight Hole Drill Collar differs from the above in that it straightens a hole when it starts to deviate from vertical, or becomes "crooked".